Method and apparatus for synchronizing timing among devices in a wireless local area network (wlan)

ABSTRACT

A wireless communication device including a first media access control device and a first transceiver. The first media access control device is configured to selectively generate a first timestamp having a first length and a second timestamp having a second length. The first timestamp indicates a first synchronization time of the wireless communication device, the second timestamp indicates only a first portion of the first synchronization time, and the first synchronization time is used by a client station to synchronize timing between the wireless communication device and the client station. The first media access control device is further configured to generate a beacon including either the first timestamp or the second timestamp, and an indication of whether the beacon includes the first timestamp or the second timestamp. The first transceiver is configured to transmit the beacon from the wireless communication device to the client station.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/902,963, filed on Nov. 12, 2013, U.S. Provisional Application No.61/928,728, filed on Jan. 17, 2014, and U.S. Provisional Application No.61/974,940, filed on Apr. 3, 2014. The entire disclosures of theapplications referenced above are incorporated herein by reference.

FIELD

The present disclosure relates to timing synchronization in wirelesslocal area networks.

BACKGROUND

Wireless local area networks (WLANs) may include an access point (AP)and one or more client stations. Various operating standards for WLANsinclude, but are not limited to, Institute for Electrical andElectronics Engineers (IEEE) 802.11a, 802.11ac, 802.11af, 802.11ah,802.11b, 802.11g, and 802.11n.

An access point periodically transmits a beacon frame at a target beacontransmission time (TBTT) and/or, in some 802.11 operating standards, ashort beacon frame at a target short beacon transmission time (TSBTT).Each of the beacon frame and the short beacon frame may include atimestamp used for a timing synchronization function (TSF). For example,each client station in a basic service set (BSS) of the WLAN may use thetimestamp in a beacon frame to synchronize timing between the AP and theclient station. FIG. 1A shows an example beacon frame 100. FIG. 1B showsan example short beacon frame 104. FIG. 1C shows an example timingdiagram 108 of transmission of the beacon frames 100 at TBTTs 110 andthe short beacon frames 104 at TSBTTs 112.

The beacon frame 100 includes a media access control (MAC) headerportion 116, which includes, for example only, a frame control field120, a duration field 124, address fields 128 (e.g., including a sourceaddress, a destination address, etc.), a sequence control field 132,and, in some standards (e.g., 802.11n), a high throughput (HT) controlfield 136. The beacon frame 100 also includes a frame body field 140 anda frame check sequence (FCS) field 144. The frame body field 140includes, for example only, an 8 byte timestamp field 148, a beaconinterval field 152, a capability field 156, a service set identifier(SSID) field 160, a supported rates field 164, and a frequency hopping(FH) parameter set field 168 and other information elements associatedwith BSS operation.

The short beacon frame 104 includes a frame control field 172, aduration field 176, a source address field 180, a 4 byte timestamp field184, a change sequence field 188, a next TBTT field 192, a compressedSSID field 196, an access network options field 200, optionalinformation elements (lEs) 204, and an FCS field 208. The optional IEs204 include a short beacon compatibility element 212, which includes,for example only, an element ID field 216, a length field 220, acapability field 224, a beacon interval field 228, and a TSF completionfield 232.

SUMMARY

A wireless communication device includes a first media access controldevice and a first transceiver. The first media access control device isconfigured to selectively generate a first timestamp having a firstlength and a second timestamp having a second length. The firsttimestamp indicates a first synchronization time of the wirelesscommunication device, the second timestamp indicates only a firstportion of the first synchronization time, and the first synchronizationtime is used by a client station to synchronize timing between thewireless communication device and the client station. The first mediaaccess control device is further configured to generate a beaconincluding either the first timestamp or the second timestamp, and anindication of whether the beacon includes the first timestamp or thesecond timestamp. The first transceiver is configured to transmit thebeacon from the wireless communication device to the client station.

A method of operating wireless communication device includes selectivelygenerating a first timestamp having a first length and a secondtimestamp having a second length. The first timestamp indicates a firstsynchronization time of the wireless communication device, the secondtimestamp indicates only a first portion of the first synchronizationtime, and the first synchronization time is used by a client station tosynchronize timing between the wireless communication device and theclient station. The method further includes generating a beaconincluding either the first timestamp or the second timestamp and anindication of whether the beacon includes the first timestamp or thesecond timestamp, and transmitting the beacon from the wirelesscommunication device to the client station.

Further areas of applicability of the present disclosure will becomeapparent from the detailed description, the claims and the drawings. Thedetailed description and specific examples are intended for purposes ofillustration only and are not intended to limit the scope of thedisclosure.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is an example beacon frame.

FIG. 1B is an example short beacon frame.

FIG. 1C is an example timing diagram of transmission of beacon framesand short beacon frames.

FIG. 2 is an example wireless local area network.

FIG. 3 is an example media access device of a client station.

FIG. 4 is an example short beacon frame 400.

FIG. 5 is an example timing synchronization function method.

In the drawings, reference numbers may be reused to identify similarand/or identical elements.

DESCRIPTION

An 8 byte timestamp field in a frame body of a beacon frame indicates atransmission time, as transmitted from an access point (AP), of a firstbit of the 8 byte timestamp field. The transmission time corresponds toa timing synchronization function (TSF) time. The 8 byte timestamp fieldcorresponds to a non-information embedding (IE) field. For example, amedia access control (MAC) layer of the AP transmitting the beacon framemay set the 8-byte timestamp field. Conversely, a client stationreceiving the beacon frame is configured (e.g., in a MAC layer of theclient station) to perform the TSF based on the 8 byte timestamp field.For example, the client station is configured to set a timer based onthe 8 byte timestamp field.

In some IEEE 802.11 standards (e.g., 802.11ah), an AP may selectivelytransmit a beacon frame (i.e., a full beacon frame) and/or a shortbeacon frame. The short beacon frame may only include a 4 bytetimestamp. For example only, an AP may transmit the short beacon frameonly at a target short beacon transmission time (TSBTT), or at both theTSBTT and a target beacon transmission time (TBTT).

For example, when transmitted at the TBTT, the 4 byte timestamp in theshort beacon frame corresponds to the least significant 4 bytes of theactual 8 byte TSF time. The 4 byte timestamp may be contained in anon-IE portion of the short beacon frame. Conversely, the mostsignificant 4 bytes of the 8 byte TSF time are contained in a TSFcompletion field in a short beacon compatibility element (as set by thetransmitting AP) of the short beacon frame. The short beaconcompatibility element is contained in an IE portion of the short beaconframe. Accordingly, the MAC layer of the client station is not able toperform the TSF until both the 4 byte timestamp field and the TSFcompletion field of the short beacon frame are received. Conversely,when transmitted at the TSBTT, the short beacon frame only includes the4 byte timestamp field corresponding to the least significant 4 bytes ofthe actual 8 byte TSF time in the non-IE portion of the short beaconframe.

When the least significant 4 bytes of the TSF time are initiallyreceived and processed by the MAC layer of the client station, acorresponding timer value is set with the value of the least significant4 bytes. However, the timer value continues to increment until the mostsignificant 4 bytes of the TSF time in the TSF completion field arereceived. In some circumstances, the timer value may increment fromFFFFFFFF to Ser. No. 00/000,000 prior to the most significant 4 bytesbeing received (i.e., the timer value may roll over, or wrap).Accordingly, calculating the actual 8 byte TSF time using the separatelyreceived least significant 4 bytes and most significant 4 bytes of the 8byte TSF time may be complicated.

Systems and methods according to the principles of the presentdisclosure provide a timestamp indication bit (e.g., in a frame controlor other non-IE field of the short beacon frame). The timestampindication bit identifies a format of the timestamp field. For example,the timestamp indication bit identifies whether the timestamp fieldincludes the entire 8 byte TSF time or only the least significant 4bytes of the TSF time. At the TBTT, the short beacon frame includes the8 byte TSF time in the timestamp field. Conversely, at the TSBTT, theshort beacon frame includes the least significant 4 bytes of the TSFtime and the client station is configured to determine the actual TSFtime using only the least significant 4 bytes. Accordingly, the TSFcompletion field can be eliminated (i.e., removed from the short beaconcompatibility element).

FIG. 2 shows an example wireless local area network (WLAN) 236 includingone or more wireless communication devices configured to implement TSFtime systems and methods according to an embodiment of the presentdisclosure. The WLAN 236 includes an access point (AP) 240 having a hostprocessor 244 in communication with a network interface 248. The networkinterface 248 includes a medium access control (MAC) device 252 and aphysical layer (PHY) device 256. The PHY device 256 includes one or moretransceivers 260-1, 260-2, . . . , and 260-n, referred to collectivelyas transceivers 260. The transceivers 260 communicate with respectiveantennas 264-1, 264-2, . . . , and 264-n, referred to collectively asantennas 264.

The AP 240 communicates with a plurality of client stations 268-1,268-2, 268-3, . . . , and 268-n, referred to collectively as clientstations 268. The client station 268-1 includes a host processor 272 incommunication with a network interface 276. The network interface 276includes a MAC device 280 and a PHY device 284. The PHY device 284includes one or more transceivers 288-1, 288-2, . . . , and 288-n,referred to collectively as transceivers 288. The transceivers 288communicate with respective antennas 292-1, 292-2, . . . , and 292-n,referred to collectively as antennas 292. One or more of the clientstations 268 may have a same or similar structure as the client station268-1. For example only, each of the client stations 268 may have a sameor different number of the transceivers 288 and the antennas 292.

The host processor 244, the MAC device 252, and/or the PHY device 256 ofthe AP 240 may be configured to generate beacon frames and short beaconframes for transmission to the respective client stations 268 (e.g., viathe transceivers 260 and the respective antennas 264). For example, theMAC device 252 of the AP 240 generates and inserts either a 4 bytetimestamp (e.g., in a short beacon frame for transmission at a TBTT) oran 8 byte timestamp (e.g., in a short beacon frame for transmission at aTSBTT) in a timestamp field of the short beacon frame and selectivelysets a timestamp indication bit to indicate whether the timestamp fieldincludes the 4 byte or the 8 byte timestamp. In an embodiment, the MACdevice 252 generates and inserts the timestamp in the timestamp fieldusing only hardware (i.e., not software) components. In embodiments, adevice, controller, etc. other than the MAC device 252 may generate andinsert the timestamp.

The client stations 268 each set their respective TSF times based on the4 byte or the 8 byte timestamp field in the short beacon frame receivedfrom the AP 240. For example, the MAC device 280 sets the TSF timeaccording to the timestamp indication bit and the timestamp field. Inembodiments, a device, controller, etc. other than the MAC device 280may set the TSF time according to the timestamp indication bit and thetimestamp field.

FIG. 3 shows an example MAC device 300 of a client station according toan embodiment. For example, the MAC device 300 corresponds to the MACdevice 280 of the client station 268-1. The MAC device 300 includes apacket receiving module 304, a MAC control module 308, and a TSF module312. The packet receiving module 304 receives, via a PHY device (e.g.,the PHY device 284), packets transmitted to the client station from anAP. For example, the packet may include a beacon, such as a short beaconframe according to embodiments of the present disclosure. The packetreceiving module 304 processes the short beacon frame and providesinformation about and/or included in the short beacon frame to the MACcontrol module 308. For example, the MAC control module 308 receives,inter alia, the timestamp indication bit and the timestamp field.

The MAC control module 308 sets the TSF time of the client stationaccording to the timestamp indication bit and the timestamp field. Forexample, if the timestamp indication bit indicates that the timestampfield includes an 8 byte timestamp, the MAC control module 308 maysimply set the TSF time of the client station to the 8 byte timestamp.For example only, the TSF module 312 may include a timer that stores andincrements an 8 byte value that corresponds to the TSF time of theclient station. Accordingly, the MAC control module 308 may set the 8byte value of the timer to the 8 byte timestamp in the timestamp field.

Conversely, if the timestamp indication bit indicates that the timestampfield includes a 4 byte timestamp, the MAC control module 308 may setonly the least significant 4 bytes of the 8 byte value of the timer tothe 4 byte timestamp. The MAC control module 308 also selectivelyincrements or decrements the most significant 4 bytes of the 8 bytevalue based on a comparison between the 4 byte timestamp received in theshort beacon frame and the least significant 4 bytes of the 8 byte valueof the timer as described below in more detail.

FIG. 4 shows an example short beacon frame 400 according to anembodiment. The short beacon frame 400 includes a frame control field404, a duration field 408, a source address field 412, a 4 or 8 bytetimestamp field 416, a change sequence field 420, a next TBTT field 424,a compressed SSID field 428, an access network options field 432, anoptional information embedding (IE) field 436, and an FCS field 440. Theoptional IE field 436 includes, but is not limited to, one or more shortbeacon compatibility elements 444, which includes, for example only, anelement ID field 448, a length field 452, a capability field 456, and abeacon interval field 460. The short beacon compatibility element doesnot include a TSF completion field.

The frame control field 404 includes a protocol version field 464, atype field 468, a subtype field 472, a next TBTT present field 476, anSSID present field 480, an interworking present field 484, a BSS BW(bandwidth) field 488, a security field 492, and a timestamp indicationfield (i.e., a timestamp indication bit) 496. In an embodiment, thetimestamp indication field 496 includes a single bit that indicateswhether the timestamp field 416 includes a 4 byte timestamp or an 8 bytetimestamp. Accordingly, when the MAC device 280 of the receiving clientstation 268-1 receives the timestamp indication field 496, the MACdevice 280 can determine whether the timestamp field 416 includes the 4byte timestamp or the 8 byte timestamp. For example only, a “0” in thetimestamp indication field 496 may indicate that the timestamp field 416includes the 4 byte timestamp while a “1” in the timestamp indicationfield 496 may indicate that the timestamp field 416 includes the 8 bytetimestamp.

For example only, the timestamp indication field 496 corresponds to bit15 of the frame control field 404, though other bits in the short beaconframe 400 may be used. In some protocols, bit 15 of the frame controlfield 404 indicates a 1 MHz primary channel position. However, anotherfield may already include an indication of the 1 MHz primary channelposition, allowing bit 15 of the frame control field 404 to be used forthe timestamp indication field 496.

When the short beacon frame 400 includes the 8 byte timestamp (i.e., asreceived at TBTT), the MAC device 280 of the receiving client station268-1 does not need to perform any additional calculation since the 8byte timestamp directly corresponds to the TSF time of the AP 240.Accordingly, the MAC device 280 sets a TSF time (e.g., a TSF timer thatstores and increments an 8 byte timer value) of the receiving clientstation 268-1 to the 8 byte timestamp in the short beacon frame 400.

Conversely, if the AP 240 prepares the short beacon frame 400 includingthe 4 byte timestamp (i.e., as received at TSBTT), the TSF time of theAP 240 corresponds to a most significant 4 bytes and the 4 bytetimestamp included in the short beacon frame 400. Accordingly, the 4byte timestamp in the short beacon frame 400 only corresponds to theleast significant 4 bytes of the entire 8 byte TSF time of the AP 240.When the MAC device 280 receives the short beacon frame 400 includingthe 4 byte timestamp, the MAC device 280 sets the least significant 4bytes of the TSF time of the receiving client station 268-1 to the 4byte timestamp. The updated TSF time of the receiving client station268-1 corresponds to the most significant 4 bytes of the TSF timemaintained by the TSF timer (e.g., according to a clock of the receivingclient station 268-1) combined with the least significant 4 bytes of theTSF time received via the 4 byte timestamp.

Accordingly, if the short beacon frame 400 includes only the 4 bytetimestamp, the TSF time of the receiving client station 268-1 matches(i.e., is the same as) the TSF time of the AP 240 if the mostsignificant 4 bytes of the respective TSF times are the same. However,in some situations, the most significant 4 bytes of the TSF time of thereceiving client station 268-1 may increment to a different value thanthe most significant 4 bytes of the TSF time of the AP 240. Systems andmethods according to an embodiment of the present disclosure correct anydiscrepancies between the respective TSF times of the receiving clientstation 268-1 and the AP 240.

For example, respective clocks of the receiving client station 268-1 andthe AP 240 may be slightly different. Accordingly, when the MAC device280 sets the TSF time of the receiving client station 268-1 using the 8byte timestamp (i.e., upon receiving the short beacon frame 400 at aTBTT), the timestamp of the receiving client station 268-1 matches thetimestamp of the AP 240. However, the difference between the clocks ofthe receiving client station 268-1 and the AP 240 may cause therespective most significant 4 bytes of the TSF times to differ at asubsequent TSBTT (i.e., when a short beacon frame including a 4 bytetimestamp is transmitted from the AP 240 to the receiving client station268-1). However, the absolute value of a difference between the TSFtimes of the receiving client station 268-1 and the AP 240 may be lessthan FFFFFFFF/2.

Accordingly, if the 4 byte timestamp included in the short beacon frame400 is, for example only, 000000FF (i.e., the least significant 4 bytesof the TSF time of the AP 240) and a current least significant 4 bytesof the TSF time of the receiving client station 268-1 is FFFFFF00, thenthe clock (and TSF time) of the AP 240 is faster than the clock (and TSFtime) of the receiving client station 268-1, and therefore the mostsignificant 4 bytes of the TSF time of the AP 240 is 1 greater than themost significant 4 bytes of the TSF time of the receiving client station268-1.

In other words, the 4 byte timestamp of 000000FF indicates that theleast significant 4 bytes of the 4 byte timestamp “rolled over” (i.e.,incremented from FFFFFFFF to Ser. No. 00/000,001 . . . 000000FF, etc.),causing the most significant 4 bytes of the TSF time of the AP 240 toincrement by 1. Accordingly, if the 4 byte timestamp received in theshort beacon frame 400 indicates that the least significant 4 bytes ofthe TSF time of the AP 240 recently rolled over, then the MAC 280 setsthe least significant 4 bytes of the TSF time of the receiving clientstation 268-1 to the 4 byte timestamp and increments the mostsignificant 4 bytes of the TSF time of the receiving client station268-1 by 1.

More specifically, when the 4 byte timestamp is received, the MAC 280determines: (i) whether the most significant bit in the 4 byte timestampis different than the most significant bit of the least significant 4bytes of the TSF time of the receiving client station 268-1; (ii)whether the 4 byte timestamp is less than the least significant 4 bytesof the TSF time of the receiving client station 268-1; and (iii) whethera difference between the 4 byte timestamp and the least significant 4bytes of the TSF time of the receiving client station 268-1 is greaterthan a predetermined threshold. For example only, the predeterminedthreshold corresponds to an expected maximum difference between the TSFtimes of the receiving client station 268-1 and the AP 240 (e.g.,FFFFFFFF/2, or 2̂31). If (i), (ii), and (iii) are true, then the MAC 280increments the most significant 4 bytes of the TSF time of the receivingclient station 268-1 by 1.

For example, as described above, a 4 byte timestamp of 000000FF in ashort beacon and a least significant 4 bytes of the TSF time of thereceiving client station 268-1 of FFFFFFF0 meets each of (i), (ii), and(iii), and therefore the MAC 280 increments the most significant 4 bytesof the TSF time of the receiving client station 268-1 by 1. Conversely,a 4 byte timestamp of FFFFFFFF in a short beacon and a least significant4 bytes of the TSF time of the receiving client station 268-1 ofFFFFFF00 does not meet each of (i), (ii), and (iii), and therefore theMAC 280 would not increment the most significant 4 bytes of the TSF timeof the receiving client station 268-1 by 1. Instead, the MAC 280 wouldonly set the least significant 4 bytes of the TSF time of the receivingclient station 268-1 to FFFFFFFF.

Conversely, if the 4 byte timestamp included in the short beacon frame400 is, for example only, FFFFFF00 (i.e., the least significant 4 bytesof the TSF time of the AP 240) and a current least significant 4 bytesof the TSF time of the receiving client station 268-1 is 0000000F, thenthe clock (and TSF time) of the AP 240 is slower than the clock (and TSFtime) of the receiving client station 268-1, and therefore the mostsignificant 4 bytes of the TSF time of the AP 240 is 1 less than themost significant 4 bytes of the TSF time of the receiving client station268-1.

In other words, the least significant 4 bytes of the TSF time of thereceiving client station 268-1 of 0000000F indicates that the leastsignificant 4 bytes rolled over, causing the most significant 4 bytes ofthe TSF time of the receiving client station 268-1 to increment by 1.Accordingly, if the 4 byte timestamp received in the short beacon frame400 indicates that the least significant 4 bytes of the TSF time of theAP 240 did not roll over but the least significant 4 bytes of the TSFtime of the receiving client station 268-1 did roll over, then the MAC280 sets the least significant 4 bytes of the TSF time of the receivingclient station 268-1 to the 4 byte timestamp and decrements the mostsignificant 4 bytes of the TSF time of the receiving client station268-1 by 1.

More specifically, when the 4 byte timestamp is received, the MAC 280determines, in addition to (i), (ii), and (iii) as described above: (iv)whether the 4 byte timestamp in a short beacon is greater than the leastsignificant 4 bytes of the TSF time of the receiving client station268-1; and (v) whether the difference between the 4 byte timestamp andthe least significant 4 bytes of the TSF time of the receiving clientstation 268-1 is greater than the predetermined threshold. If (i), (iv),and (v) are true, then the MAC 280 decrements the most significant 4bytes of the TSF time of the receiving client station 268-1 by 1.

For example, as described above, a 4 byte timestamp of FFFFFF00 and aleast significant 4 bytes of the TSF time of the receiving clientstation 268-1 of 0000000F meets each of (i), (iv), and (v), andtherefore the MAC 280 decrements the most significant 4 bytes of the TSFtime of the receiving client station 268-1 by 1. Conversely, a 4 bytetimestamp of FFFFFF00 and a least significant 4 bytes of the TSF time ofthe receiving client station 268-1 of FFFFFFFF does not meet each of(i), (iv), and (v), and therefore the MAC 280 would not decrement themost significant 4 bytes of the TSF time of the receiving client station268-1 by 1. Instead, the MAC 280 would only set the least significant 4bytes of the TSF time of the receiving client station 268-1 to FFFFFF00.

FIG. 5 shows and example TSF method 500 according to an embodiment ofthe present disclosure. The method 500 begins at 504. At 508, a clientstation receives, at a TBTT or a TSBTT, a short beacon frame includingan 8 byte timestamp or a 4 byte timestamp. For example, the receivingclient station 268-1 receives the short beacon frame 400 from the AP240. At 512, the client station determines whether the short beaconframe includes an 8 byte timestamp. For example, a MAC (e.g., the MAC280) determines whether a timestamp indication bit in the short beaconframe is set (e.g., where the bit being set indicates the 8 bytetimestamp and the bit not being set indicates the 4 byte timestamp). Iftrue, the method 500 continues to 516. If false, the method 500continues to 520. At 516, the MAC of the client station sets its TSFtime to the 8 byte timestamp and the method 500 continues to 508.

At 520, the MAC of the client station determines whether a mostsignificant bit of the 4 byte timestamp and the most significant bit ofthe least significant 4 bytes of the TSF time of the client station aredifferent. If true, the method 500 continues to 524. If false, themethod 500 continues to 528. At 528, the MAC of the client station setsthe least significant 4 bytes of its TSF time to the 4 byte timestampand the method 500 continues to 508.

At 524, the MAC of the client station determines whether the 4 bytetimestamp is less than the least significant 4 bytes of the TSF time ofthe client station. If true, the method 500 continues to 532. If false,the method 500 continues to 536. At 532, the MAC of the client stationdetermines whether a difference between the least significant 4 bytes ofthe TSF time of the client station and the 4 byte timestamp is greaterthan a predetermined threshold (e.g., 2̂31). If true, the method 500continues to 540. If false, the method 500 continues to 544. At 540, theMAC of the client station increments the most significant 4 bytes of theTSF time of the client station by 1 and the method 500 continues to 544.At 544, the MAC of the client station sets the least significant 4 bytesof the TSF time of the client station to the 4 byte timestamp and themethod 500 continues to 508.

At 536, the MAC of the client station determines whether a differencebetween the 4 byte timestamp and the least significant 4 bytes of theTSF time of the client station is greater than the predeterminedthreshold. If true, the method 500 continues to 548. If false, themethod 500 continues to 528. At 548, the MAC of the client stationdecrements the most significant 4 bytes of the TSF time of the clientstation by 1 and the method 500 continues to 528. At 528, the MAC of theclient station sets the least significant 4 bytes of the TSF time of theclient station to the 4 byte timestamp and the method 500 continues to508.

The wireless communications described in the present disclosure can beconducted in full or partial compliance with IEEE standard 802.11-2012,IEEE standard 802.16-2009, IEEE standard 802.20-2008, and/or BluetoothCore Specification v4.0. In various implementations, Bluetooth CoreSpecification v4.0 may be modified by one or more of Bluetooth CoreSpecification Addendums 2, 3, or 4. In various implementations, IEEE802.11-2012 may be supplemented by draft IEEE standard 802.11ac, draftIEEE standard 802.11ad, and/or draft IEEE standard 802.11ah.

The foregoing description is merely illustrative in nature and is in noway intended to limit the disclosure, its application, or uses. Thebroad teachings of the disclosure can be implemented in a variety offorms. Therefore, while this disclosure includes particular examples,the true scope of the disclosure should not be so limited since othermodifications will become apparent upon a study of the drawings, thespecification, and the following claims. As used herein, the phrase atleast one of A, B, and C should be construed to mean a logical (A OR BOR C), using a non-exclusive logical OR, and should not be construed tomean “at least one of A, at least one of B, and at least one of C.” Itshould be understood that one or more steps within a method may beexecuted in different order (or concurrently) without altering theprinciples of the present disclosure.

The apparatuses and methods described in this application may bepartially or fully implemented by a special purpose computer created byconfiguring a general purpose computer to execute one or more particularfunctions embodied in computer programs. The computer programs includeprocessor-executable instructions that are stored on at least onenon-transitory, tangible computer-readable medium. The computer programsmay also include or rely on stored data. The computer programs mayinclude a basic input/output system (BIOS) that interacts with hardwareof the special purpose computer, device drivers that interact withparticular devices of the special purpose computer, one or moreoperating systems, user applications, background services andapplications, etc.

The computer programs may include: (i) assembly code; (ii) object codegenerated from source code by a compiler; (iii) source code forexecution by an interpreter; (iv) source code for compilation andexecution by a just-in-time compiler, (v) descriptive text for parsing,such as HTML (hypertext markup language) or XML (extensible markuplanguage), etc. As examples only, source code may be written in C, C++,C#, Objective-C, Haskell, Go, SQL, Lisp, Java®, ASP, Perl, Javascript®,HTML5, Ada, ASP (active server pages), Perl, Scala, Erlang, Ruby,Flash®, Visual Basic®, Lua, or Python®.

None of the elements recited in the claims is intended to be ameans-plus-function element within the meaning of 35 U.S.C. §112(f)unless an element is expressly recited using the phrase “means for”, orin the case of a method claim using the phrases “operation for” or “stepfor”.

1. A wireless communication device, comprising: a first media accesscontrol device configured to selectively generate (i) a first timestamphaving a first length, and (ii) a second timestamp having a secondlength, wherein the first timestamp indicates a first synchronizationtime of the wireless communication device, wherein the second timestampindicates only a first portion of the first synchronization time, andwherein the first synchronization time is used by a client station tosynchronize timing between the wireless communication device and theclient station, and generate a beacon including (i) either the firsttimestamp or the second timestamp, and (ii) an indication of whether thebeacon includes the first timestamp or the second timestamp, wherein theindication of whether the beacon includes the first timestamp or thesecond timestamp corresponds to a timestamp indication bit in a framecontrol field of the beacon; and a first transceiver configured totransmit the beacon from the wireless communication device to the clientstation.
 2. The wireless communication device of claim 1, wherein thewireless communication device corresponds to an access point.
 3. Thewireless communication device of claim 1, wherein the first length isgreater than the second length.
 4. The wireless communication device ofclaim 1, wherein the first length is 8 bytes and the second length is 4bytes.
 5. (canceled)
 6. The wireless communication device of claim 1,wherein the first media access control device is configured to generatethe beacon including the first timestamp at a target beacon transmissiontime.
 7. The wireless communication device of claim 1, wherein the firstmedia access control device is configured to generate the beaconincluding the second timestamp at a target short beacon transmissiontime.
 8. The wireless communication device of claim 1, wherein thebeacon corresponds to a short beacon frame.
 9. A system comprising (i)the wireless communication device of claim 1 and (ii) the clientstation, wherein the client station comprises: a second transceiverconfigured to receive the beacon transmitted from the wirelesscommunication device to the client station; and a second media accesscontrol device configured to determine, based on the indication, whetherthe beacon includes the first timestamp or the second timestamp, if thebeacon includes the first timestamp, set a second synchronization timeof the client station to the first timestamp, and if the beacon includesthe second timestamp, (i) set only a first portion of the secondsynchronization time to the first portion of the first synchronizationtime corresponding to the second timestamp and (ii) selectivelyincrement or decrement, based on a comparison between the secondtimestamp and the first portion of the second synchronization time, asecond portion of the second synchronization time.
 10. The system ofclaim 9, wherein (i) the first portion of the second synchronizationtime corresponds to a least significant 4 bytes of the secondsynchronization time, (ii) the second portion of the secondsynchronization time corresponds to a most significant 4 bytes of thesecond synchronization time, and (iii) the first portion of the firstsynchronization time corresponds to a least significant 4 bytes of thefirst synchronization time.
 11. The system of claim 9, wherein, todetermine whether to selectively increment or decrement the secondportion of the second synchronization time, the second media accesscontrol device is configured to (i) determine whether a most significantbit of the first portion of the second synchronization time and a mostsignificant bit of the second timestamp are different, (ii) determinewhether the second timestamp is greater than or less than the firstportion of the second synchronization time, and (iii) determine whethera difference between the second timestamp and the first portion of thesecond synchronization time is greater than a predetermined threshold.12. A method of operating wireless communication device, the methodcomprising: selectively generating (i) a first timestamp having a firstlength, and (ii) a second timestamp having a second length, wherein thefirst timestamp indicates a first synchronization time of the wirelesscommunication device, wherein the second timestamp indicates only afirst portion of the first synchronization time, and wherein the firstsynchronization time is used by a client station to synchronize timingbetween the wireless communication device and the client station;generating a beacon including (i) either the first timestamp or thesecond timestamp, and (ii) an indication of whether the beacon includesthe first timestamp or the second timestamp, wherein the indication ofwhether the beacon includes the first timestamp or the second timestampcorresponds to a timestamp indication bit in a frame control field ofthe beacon; and transmitting the beacon from the wireless communicationdevice to the client station.
 13. The method of claim 12, wherein thewireless communication device corresponds to an access point.
 14. Themethod of claim 12, wherein the first length is greater than the secondlength.
 15. The method of claim 12, wherein the first length is 8 bytesand the second length is 4 bytes.
 16. (canceled)
 17. The method of claim12, wherein generating the beacon includes generating the beaconincluding the first timestamp at a target beacon transmission time. 18.The method of claim 12, wherein generating the beacon includesgenerating the beacon including the second timestamp at a target shortbeacon transmission time.
 19. The method of claim 12, wherein the beaconcorresponds to a short beacon frame.
 20. The method of claim 12, furthercomprising, using the client station: receiving the beacon transmittedfrom the wireless communication device to the client station;determining, based on the indication, whether the beacon includes thefirst timestamp or the second timestamp; if the beacon includes thefirst timestamp, setting a second synchronization time of the clientstation to the first timestamp; and if the beacon includes the secondtimestamp, setting only a first portion of the second synchronizationtime to the first portion of the first synchronization timecorresponding to the second timestamp, and selectively incrementing ordecrementing, based on a comparison between the second timestamp and thefirst portion of the second synchronization time, a second portion ofthe second synchronization time.